Ecological rather than geographic or genetic distance affects local adaptation of the rare perennial herb, Aster amellus

Transferring plants between populations of rare species has often been proposed to increase population size and replenish genetic variation. While this approach has many advantages, it may also disrupt local adaptation. However, the scale over which plants adapt to local conditions is hard to predict. To detect local adaptation, we conducted reciprocal transplant experiments in the field with six populations of the rare perennial herb, Aster amellus. We sowed seeds in 2003 and 2004 (called ‘Experiment 2003’ and ‘Experiment 2004’) and transplanted adult plants in 2004. We evaluated genetic differences between populations and ecological differences between habitats and tested which differences explain the degree of local adaptation. The number of juveniles from the local populations was 68% and 42% higher than the number of juveniles from the foreign populations in ‘Experiment 2003’ and ‘Experiment 2004’, respectively, indicating local adaptation. However, not all populations of A. amellus adapted to their local conditions. Differences in local climate and in vegetation composition particularly affected local adaptation. In contrast to transplanted seeds, transplanted adult plants from local populations did not overall perform better than plants from foreign populations. We conclude that transfer of seeds is a more appropriate technique than transfer of adult plants in conservation practice because it more likely prevents non-adapted genotypes from establishing. Material for the transfers should come, not necessarily from the closest, but rather from ecologically similar habitats.